Use of a crystal for nonlinear frequency conversion of a laser beam is well known. Common crystals used for this purpose include LBO (lithium triborate) and KTP (potassium titanylphosphate) having the shape of a rectangular parallelepiped. In one known application, infrared laser light having a wavelength of about one micron enters the crystal and green laser light having a wavelength of about five hundred nanometers exits the crystal. The harmonic-generation performance of the crystal depends on its temperature, and typically the crystal is heated to a constant temperature of up to generally 200 degrees Celsius. A known stand-alone oven design supports the crystal by rigidly pressing the crystal against one temperature-controlled surface.